Dataset Information

Sensing Living Bacteria in Vivo Using d-Alanine-Derived ¹¹C Radiotracers.

ABSTRACT: Incorporation of d-amino acids into peptidoglycan is a unique metabolic feature of bacteria. Since d-amino acids are not metabolic substrates in most mammalian tissues, this difference can be exploited to detect living bacteria in vivo. Given the prevalence of d-alanine in peptidoglycan muropeptides, as well as its role in several antibiotic mechanisms, we targeted this amino acid for positron emission tomography (PET) radiotracer development. d-[3-¹¹C]Alanine and the dipeptide d-[3-¹¹C]alanyl-d-alanine were synthesized via asymmetric alkylation of glycine-derived Schiff-base precursors with [¹¹C]methyl iodide in the presence of a cinchonidinium phase-transfer catalyst. In cell experiments, both tracers showed accumulation by a wide variety of both Gram-positive and Gram-negative pathogens including Staphylococcus aureus and Pseudomonas aeruginosa. In a mouse model of acute bacterial myositis, d-[3-¹¹C]alanine was accumulated by living microorganisms but was not taken up in areas of sterile inflammation. When compared to existing clinical nuclear imaging tools, specifically 2-deoxy-2-[¹⁸F]fluoro-d-glucose and a gallium citrate radiotracer, d-alanine showed more bacteria-specific uptake. Decreased d-[3-¹¹C]alanine uptake was also observed in antibiotic-sensitive microbes after antimicrobial therapy, when compared to that in resistant organisms. Finally, prominent uptake of d-[3-¹¹C]alanine uptake was seen in rodent models of discitis-osteomyelitis and P. aeruginosa pneumonia. These data provide strong justification for clinical translation of d-[3-¹¹C]alanine to address a number of important human infections.

SUBMITTER: Parker MFL

PROVIDER: S-EPMC7047270 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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Publications

Sensing Living Bacteria in Vivo Using d-Alanine-Derived 11C Radiotracers.

Parker Matthew F L MFL Luu Justin M JM Schulte Brailee B Huynh Tony L TL Stewart Megan N MN Sriram Renuka R Yu Michelle A MA Jivan Salma S Turnbaugh Peter J PJ Flavell Robert R RR Rosenberg Oren S OS Ohliger Michael A MA Wilson David M DM

ACS central science 20200204 2

Incorporation of d-amino acids into peptidoglycan is a unique metabolic feature of bacteria. Since d-amino acids are not metabolic substrates in most mammalian tissues, this difference can be exploited to detect living bacteria in vivo. Given the prevalence of d-alanine in peptidoglycan muropeptides, as well as its role in several antibiotic mechanisms, we targeted this amino acid for positron emission tomography (PET) radiotracer development. d-[3-11C]Alanine and the dipeptide ...[more]

PMID: 32123733

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Project description:Tau aggregates and amyloid-? (A?) plaques are key histopathologic features in Alzheimer disease (AD) and are considered targets for therapeutic intervention as well as biomarkers for diagnostic in vivo imaging agents. This article describes the preclinical in vitro and in vivo characterization of 3 novel compounds-RO6958948, RO6931643, and RO6924963-that bind specifically to tau aggregates and have the potential to become PET tracers for future human use. Methods: RO6958948, RO6931643, and RO6924963 were identified as high-affinity competitors at the 3H-T808 binding site on native tau aggregates in human late-stage AD brain tissue. Binding of tritiated compounds to brain tissue sections of AD patients and healthy controls was analyzed by macro- and microautoradiography and by costaining of tau aggregates and A? plaques on the same tissue section using specific antibodies. All 3 tracer candidates were radiolabeled with a PET nuclide and tested in vivo in tau-naïve baboons to assess brain uptake, distribution, clearance, and metabolism. Results:3H-RO6958948, 3H-RO6931643, and 3H-RO6924963 bound with high affinity and specificity to tau aggregates, clearly lacking affinity for concomitant A? plaques in human AD Braak V tissue sections. The specificity of all 3 radioligands for tau aggregates was supported, first, by binding patterns in AD sections comparable to the tau-specific radioligand 3H-T808; second, by very low nonspecific binding in brain tissue devoid of tau pathology, excluding significant radioligand binding to any other central nervous system target; and third, by macroscopic and microscopic colocalization and quantitative correlation of radioligand binding and tau antibody staining on the same tissue section. RO6958948, RO6931643, and RO6924963 were successfully radiolabeled with a PET nuclide at high specific activity, radiochemical purity, and yield. After intravenous administration of 18F-RO6958948, 11C-RO6931643, and 11C-RO6924963 to baboons, PET scans indicated good brain entry, rapid washout, and a favorable metabolism pattern. Conclusion:18F-RO6958948, 11C-RO6931643, and 11C-RO6924963 are promising PET tracers for visualization of tau aggregates in AD. Head-to-head comparison and validation of these tracer candidates in AD patients and healthy controls will be reported in due course.

Project description:BackgroundFibroblast activation protein (FAP) is a proline selective serine protease that is overexpressed in tumor stroma and in lesions of many other diseases that are characterized by tissue remodeling. In 2014, a most potent FAP-inhibitor (referred to as UAMC1110) with low nanomolar FAP-affinity and high selectivity toward related enzymes such as prolyl oligopeptidase (PREP) and the dipeptidyl-peptidases (DPPs): DPP4, DPP8/9 and DPP2 were developed. This inhibitor has been adopted recently by other groups to create radiopharmaceuticals by coupling bifunctional chelator-linker systems. Here, we report squaric acid (SA) containing bifunctional DATA5m and DOTA chelators based on UAMC1110 as pharmacophor. The novel radiopharmaceuticals DOTA.SA.FAPi and DATA5m.SA.FAPi with their non-radioactive derivatives were characterized for in vitro inhibitory efficiency to FAP and PREP, respectively and radiochemical investigated with gallium-68. Further, first proof-of-concept in vivo animal study followed by ex vivo biodistribution were determined with [68Ga]Ga-DOTA.SA.FAPi.Results[68Ga]Ga-DOTA.SA.FAPi and [68Ga]Ga-DATA5m.SA.FAPi showed high complexation >?97% radiochemical yields after already 10?min and high stability over a period of 2?h. Affinity to FAP of DOTA.SA.FAPi and DATA5m.SA.FAPi and its natGa and natLu-labeled derivatives were excellent resulting in low nanomolar IC50 values of 0.7-1.4?nM. Additionally, all five compounds showed low affinity for the related protease PREP (high IC50 with 1.7-8.7??M). First proof-of-principle in vivo PET-imaging animal studies of the [68Ga]Ga-DOTA.SA.FAPi precursor in a HT-29 human colorectal cancer xenograft mouse model indicated promising results with high accumulation in tumor (SUVmean of 0.75) and low background signal. Ex vivo biodistribution showed highest uptake in tumor (5.2%ID/g) at 60?min post injection with overall low uptake in healthy tissues.ConclusionIn this work, novel PET radiotracers targeting fibroblast activation protein were synthesized and biochemically investigated. Critical substructures of the novel compounds are a squaramide linker unit derived from the basic motif of squaric acid, DOTA and DATA5m bifunctional chelators and a FAP-targeting moiety. In conclusion, these new FAP-ligands appear promising, both for further research and development as well as for first human application.

Dataset Information

Sensing Living Bacteria in Vivo Using d-Alanine-Derived ¹¹C Radiotracers.

Publications

Sensing Living Bacteria <i>in Vivo</i> Using d-Alanine-Derived <sup>11</sup>C Radiotracers.

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